Add Wandering Vendors.

These are basically wandering Vendors who walk around the world, usually along the roads selling upmarket
rare items .
The Items would be limited supply, ie the vendor only has a small number to sell, and once sold , no more could be purchased for a random time.
The Vendors would randomly appear and dissapear, so coudnt be easily camped, and the random items being sold would also randomly change.
The Vendors could be attacked by Mobs and killed, and would only set up their shop when they reached a camp or town, so there would be incentive for players to help keep the Vendors alive.

There are actually a few vendors along these lines in the game, they just don't play particularly prominent roles.

Gloamwood has one that can appear in multiple locations, and Shimmer and Droughtlands both have their own off the top of my head. They have a handful of rare items (which aren't too special anymore, but maybe early on...), and at least the Freemarch one can indeed be killed, by players or mobs I believe.